Re-generate Coderay syntax highlighting styles [OP 3.x backport]

Coderay 1.0+ now uses more descriptive class names.
We use the default (alpha) styles:

`coderay stylesheet > app/assets/stylesheets/coderay.css`

https://community.openproject.org/work_packages/17114
@myabc The ``coderay.css`` is not correctly loaded. I was able to fix it by adding ``@import coderay`` to [``app/assets/stylesheets/default.css``](https://github.com/opf/openproject/blob/release/3.0/app/assets/stylesheets/default.css.sass). Probably, this makes this ``require`` obsolete?